linux-kernel - Re: [PATCH v2 2/2] mfd: axp20x: Fix AXP806 access errors on cold boot

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Message-ID: <20161214174053.qsm6umlgtdivevwt@sirena.org.uk>
Date:   Wed, 14 Dec 2016 17:40:53 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Lee Jones <lee.jones@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH v2 2/2] mfd: axp20x: Fix AXP806 access errors on cold boot

On Wed, Dec 14, 2016 at 09:52:31PM +0800, Chen-Yu Tsai wrote:

> What this patch does is make sure the registers match, to guarantee
> access, and then reinitialize the regmap cache to get rid of any
> stale data.

So what you're saying is that previous writes may have been ignored?

> > If the chip has been reset then you'd want to reset the cache too.  I've
> > no idea if that's needed here or not though, it depends what happens to
> > the global state of the chip when this reconfiguration happens.

> It is not a reset in the general sense. I suppose a better way would
> be to do an explicit write to the register first, then initialize
> the regmap. I'd have to export the write function from the RSB bus
> driver first though.

Surely just doing a write immediately after initializing the regmap
would have the same effect?  That'd ensure that the hardware has the
desired value before there are any other writes.  But I might be missing
something here.

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